1. Technical Field
The invention relates to a device, system, and method, for use with a rotary joint and heat transfer cylinders used typically in the papermaking process. Generally, the device, a secondary bearing support, and a stationary siphon system which may employ it, improves the reliability and efficiency of various papermaking machines.
2. Related Art
A papermaking machine typically includes three main sections: Forming, Pressing and Drying. The raw material, called furnish, is largely water, and is converted to a sheet by these three sections. The first section, Forming, uses vacuum and other means to remove most of the water. At the same time, the fibers of the sheet are formed into the desired mat. The second section, Pressing, removes more water by pressing the sheet between felted rolls. The final phase of removing water from a sheet in a paper machine relies on heated cylinders, called dryers. The Drying frequently consumes more energy than any other section of the machine and, in many cases, more than any other operation in a papermaking mill.
One manner of drying the sheet is to use heated cylinders (a.k.a. dryers or cans). These rotating cylinders are heated by a heat transfer medium, typically this may be steam. A dryer section usually includes of many cans arranged in single or multiple tiers. The sheet is threaded through this arrangement of dryers, wrapping partially around a can and passing from can to can. The sheet is heated by the rotating dryer cans and most or all of the remaining water is evaporated from the sheet.
Several factors determine the rate of evaporation, or drying, of this remaining water within the sheet. One of these factors is the rate of transfer of the heat from the steam inside the dryer can to the exterior surface of the dryer can. As the sheet contacts a dryer, and the steam within the dryer is condensing, heat is transferred from the condensing steam inside the dryer through the dryer shell and into the sheet. A principle of heat transfer is that heat moves from higher temperatures to lower ones. The rate of this transfer depends on the temperature differential and the resistance to the heat transfer. A significant resistance to the transfer of the heat is the quantity of condensed steam, or condensate, inside the can.
A rotary joint, or union, is typically used as a junction point wherein fixed parts of the system meet, or have a junction with, rotating parts of the system. The rotating parts include the can itself and portions of the rotary joint. The fixed parts include other portions of the rotary joint and fixed piping attached to the rotary joint. The steam is supplied to the inside of the can typically through a portion of the rotary joint, or union. In some cases, the condensed steam (i.e., condensate) is evacuated through another portion of the same rotary joint, while in others it is removed through a second rotary joint. Since the condensate collects inside the dryer shell or cylinder, a siphon may be employed to remove the condensate from the shell. The siphon, with its inlet, or pickup, close to the interior surface of the dryer shell, is connected to the rotary joint by a horizontal pipe. The condensate is collected at a tip of the siphon inlet. The condensate then passes into the siphon; then through the horizontal pipe; and, finally through the rotary joint and to the fixed piping connected beyond.
Multiple forces must be overcome to remove the condensate from of the can. This is accomplished, in part, by creating a pressure differential. The pressure differential is typically measured between a steam inlet port leading into the rotary joint and a condensate outlet port, also located on the rotary joint. Optimally, the condensate is removed from the can at the same rate at which it is being created from the condensing steam, while concurrently being done with the lowest possible differential pressure. During normal operating conditions, some steam will also exit the dryer in the same manner as the condensate. This exiting steam is commonly referred to as “blowthrough steam”. Blowthrough steam is undesirable.
Although condensate is being removed from the dryer can, the amount of condensate that remains in the dryer can at any time is determined, in part, by the distance between the siphon tip and the interior surface of the dryer can and the stability of this interface. The closer the siphon tip can be located to the surface of the dryer shell without contacting the shell, the more of the condensate can be removed from inside the dryer, and the smaller the quantity of condensate remains in the bottom of the inside of the dryer. Exacerbating this issue is that siphon tips also move. The siphon tip movement may be caused by movement in several areas including movement in: the rotary joint; the siphon assembly including both the horizontal and vertical pipe portions; the condensate; the rotating dryer can; paper machine vibration; or, a combination of these. Any reduction in this movement permits the siphon tip to maintain its close and consistent proximity with the condensate and to be placed closer to the interior surface of the can, thereby minimizing the amount of the condensate remaining in the can.
The behavior of the condensate inside the can is related to the rotating speed of the can. At very low speeds of rotation, the condensate puddles at the bottom of the can as a result of the forces of gravity. As the speed of rotation increases, however, the combination of centrifugal forces and the adhesion of the condensate to the interior surface of the dryer cylinder causes portions of the condensate puddle to move up the cylinder wall in the same direction as the rotation. This movement of condensate is called “puddling” or “cascading”.
During speeds when the condensate is puddling or cascading, a stationary siphon can be used. The stationary designation results from the fact that the siphon is not rotating along with the can (Cf. other siphon designs, such as rotary siphons, which have a siphon which rotates along with the can). Two beneficial features of the stationary siphon include being able to permanently position the siphon tip close to the condensate puddle, and some stationary siphons may be installed and/or removed without personnel having to enter the dryer cylinder.
Inherent to the process of removing condensate from the can with a siphon, a portion of the supplied steam will also exit. The quantity of this blowthrough steam is determined, in part, by the magnitude of the differential pressure. In part, the amount of differential pressure is dictated by the flow restrictions in the siphon-rotary joint-piping assembly. Thus, the greater the flow restrictions in the assembly, the greater the requisite differential pressure to adequately pull condensate from the can. Unfortunately, the greater the differential pressure is, the greater amount of blowthrough steam that is also removed from the can.
Another deficiency in current stationary siphon systems is mechanical in nature. The entire siphon (i.e., both the horizontal and vertical portions of pipe) frequently is only singularly attached to the interior of the rotary joint at the very end of the horizontal pipe. The siphon may also be supported additionally at a second point close to the aforementioned single point of attachment. These types of siphon connections result in a cantilever of upwards of 50 inches. The cantilever, and the long vertical reach of the vertical portion of the siphon pipe, creates a significant moment arm and resultant stresses on various parts in the rotary joint, including, inter alia, seals and bearings.
In summary, a need exists to overcome the above stated, and other, deficiencies in the art.